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Non-eliminative physicalism and model-dependent realism (and cake!)

Discussions about philosophy can be exasperating; they're often steeped in esoteric language and can seem pedantic. After all, philosophy isn't something we concern ourselves in our daily lives; we have intuitive, functional ways of going about our day that we adopt without so much as a second thought, and at first blush it seems like philosophy doesn't have much hope of changing much about the human experience. And I suppose that directly, that's true. All my years of reading and discussing philosophy certainly haven't changed much, if anything, about how I live my life on a day to day basis. But it has informed how I think, how I shape and define my beliefs, and how I communicate my ideas with others.

If that seems like an odd way to start a post with an admittedly esoteric and verbose title (I really had no idea how to make it catchy), it's because I can fully understand why someone would look at these topics with a big fat Who gives a shit? Why should you care about eliminative vs. non-eliminative physicalism? What the hell is model-dependent realism? Why should you care about ontology? Well, I can't promise that reading about this stuff will change your life. It probably won't make you a better person. But it might give you a new perspective on how we approach the acquisition of human knowledge, how we can identify erroneous ways of thinking, and what types of beliefs are justified. Because this is a lengthier-than-usual post, I've stuck in the dashes to break it up a bit.

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The correspondence theory of truth
To get to non-eliminative physicalism, I'm going to start with Aristotle, the godfather of essentialism. For Aristotle, there was no distinction between epistemology (how you know what you think you know) and ontology (what things actually are). He contended that our minds directly grasp the "essences" of things in the world, so there is no bridge between conceptual abstraction in the mind and objective truth in the world. If I say, "the cat is on the mat", I am thinking about objectively real things that have distinct categorical identities that exist objectively — that is, independently of my mind. All that is required of the mind is to grasp what is, and to even contemplate the idea of the cat on the mat is to recognize that the cat and the mat both have distinct categorical identities. In this view, the mind is not modeling the world, but simply recognizing it — the categories of the mind directly correspond to the categories of the world.

This essentialism can also be considered the roots of what is popularly called the correspondence theory of truth [1]. Put in its most simple and colloquial form, the correspondence theory simply says:

A statement is true when it fits the way things are in the world. It is false when it fails to fit the way things are in the world. [Lakoff, Philosophy in the Flesh]

This seems intuitively obvious, and the old "cat on the mat" example shows why. Most of us agree that if we are observing a cat on a mat, we are observing objects that are distinct from each other and that exist independently of our ability to perceive them. The cat has distinct cat-making properties, just as the mat has distinct mat-making properties. Moreover, we recognize "on-ness", or the state of the cat being on the mat, as being an objectively true statement about the relationship between these two objects. If I say "the cat is on the mat" while the cat is in his litter box, my statement is objectively false because my expression of the relationship between those two objects does not correspond to the way things are in the world.

Aristotle took all this a step further. While we all agree about the properties and relations of physical things like cats and mats, conceptual abstractions like "love", "truth", and "being" might seem to have a more ambiguous nature. Love is clearly not a physical thing, but most of us agree that in some sense love exists. Aristotle thought that these types of abstractions were simply different categories of being: non-physical and immaterial, but nonetheless wholly real in that distinct properties could be predicated of them. When we contemplate love, we are contemplating something non-physical but something that still has real properties (or an "essence") that our minds are simply recognizing. Love is not a construct of the mind, but a real non-physical entity in the world that the mind grasps through reason.

It might be hard to imagine why the correspondence theory of truth is loaded with some serious problems when it seems to reflect exactly how we interact with the world and know things to be true or false in a highly intuitive way. But a closer examination reveals that the correspondence theory not only leaves crucial questions unanswered, but also fails to conform to our empirical knowledge of how the mind actually works.

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The elephant in the room for the correspondence theory is how the mind grasps and expresses these relationships. According to the Aristotlean view, the mind — and reason itself — is ultimately disembodied, in that the body plays no crucial role in the formation of concepts. But this leaves us without any explanation as to how the non-physical mind is able to bridge the gap to physical objects, spatial relationships, and non-physical abstractions. Aristotle's solution is a "just-so" argument, in which the problem is wholly ignored altogether: the mind recognizes these distinct objects and relationships because it does. How is never even broached.

To see why this is problematic, I want to re-visit something I talked about in an older post: the existence of "color". According to the Aristotlean view, if I say "the painting is blue", I am expressing "blue" as an objective property of the painting. The same is true if I say that "the sky is blue". However, this conflicts with our empirical knowledge of the world. Waves of light, in themselves, do not have the property of color. We perceive color because of an interaction between the cones in our eyes and neural structures in our brains. To understand this, consider the painting and the sky both having the property of "blueness". The sky is not a solid object; it appears blue because certain wavelengths of visible light are scattered by our atmosphere. This is starkly different from why the painting is blue, which is because light is being reflected off a solid object. Moreover, whether the painting appears blue is also contingent on the wavelengths of light the object absorbs or reflects, like how an object may appear either green or blue depending on the ambient light. The correspondence theory is in trouble on both fronts: both in its inability to bridge the gap between the non-physical mind and the physical world, and in its erroneous attribution of "blueness" as an inherent property of an object.

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It gets worse, though: there are levels of "truth" which appear to be incompatible with one another. The Aristotlean view privileges a certain frame of reference: the phenomenological — that is, our everyday conscious experiences and intuitions. But as the color example demonstrates, this cannot be true.

In the phenomenological view favored by essentialism, color is a property inherent to an object. In this sense, the notion of "the painting is blue" seems intuitively true: the property of blueness is inherent to the painting. But given what we know about what color is — the aforementioned interaction between the visible electromagnetic spectrum, light cones in our eyes, and neural structures in the brain — the similar statement "the sky is blue" cannot be true. The sky is not an object, and thus cannot have an inherent property of blueness. Rather, the concept of blue must be modeled by our brains through the interaction of our embodied minds and visual cortex with the physical world.

So we have two views: a scientific, physical view that describes color as wavelengths of the electromagnetic spectrum interacting with our visual cortex; and a phenomenological view that describes color as an inherent property of objects. On the correspondence view, both cannot be true because the correspondence theory calls for a unified truth that holds at all frames of reference.

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Abstract thought and metaphor

Let's jump ship for a bit and talk about love; or rather, conceptual abstractions like love. Remember that on the correspondence view, love is a real but non-physical thing which our minds comprehend through pure reason — the body and brain play no role in constructing the concept of love.

It's worth repeating that this view fails to show, just as it did with objective physical objects and relations, how the mind recognizes these objective non-physical objects and their relations. If love is "out there" in the world simply waiting to be discovered through a disembodied process of reasoning, how does this process of discovery occur? How is the gulf between perception and existence bridged by the mind? The Aristotlean view again leaves us no answer.

But as with physical things, the problem is worse for the correspondence view with non-physical things as well. If our concept of love is a correspondence to a literally real non-physical thing, then we ought to be able to identify a definition of love that is true independently of any frame of reference. Again though, we have a scientific view of love — neural and chemical structures in the brain, responses to stimuli, and metaphorical thought — and a phenomenological view of love. Both are useful frames of reference in certain contexts, but both cannot be true under the correspondence theory of truth.

A hasty reaction would be to claim that the physical processes associated with love are merely physical correlates resulting from our embodiment, and not the formation of love itself. But we cannot even conceptualize love without using metaphorical language. Take the old Biblical scripture from 1 Corinthians:

4 Love is patient, love is kind. It does not envy, it does not boast, it is not proud.5 It does not dishonor others, it is not self-seeking, it is not easily angered, it keeps no record of wrongs.6 Love does not delight in evil but rejoices with the truth.7 It always protects, always trusts, always hopes, always perseveres.

The word is expresses a relationship meaning equal to. So if I am behaving patiently while waiting in a traffic jam (calmly listening to music instead of, say, honking my horn and yelling at strangers), does that imply that I am behaving lovingly? For most of us, love is a deeper and more complex concept than that. We associate love with some measure of selflessness, generosity, and humility. The Biblical scripture is discussing love in metaphorical terms (in this case, as an entity or force), because that is the only way love can be discussed at all.

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Frans de Waal, in a popular TED Talk, discussed (as he often does) the empathetic behavior of apes. He explained that empathy can be divided into two broad categories: a physical channel and a cognitive channel. The former is when, if for example we're consoling a grieving friend, we adopt the posture and body language that they do. This type of mimicry is common in our modern evolutionary cousins. The cognitive channel is the process of imagining ourselves in the others' place, in a sense 'feeling what they feel'. This, it appears, animals have not developed as we have.

Consider how George Lakoff, in discussing the work of Christopher Johnson, relates a similar concept to the development of abstract concepts in humans:

For example, for an infant, the subjective experience of affection is typically correlated with the sensory experience of warmth, the warmth of being held. During the period of conflation, associations are automatically built up between the two domains. Later, during a period of differentiation, children are then able to separate out the domains, but the cross-domain associations persist. These persisting associations are the mappings of conceptual metaphor that will lead the same infant, later in life, to speak of "a warm smile," "a big problem," and "a close friend."¹

It appears that many animals (who, not coincidentally, have in some cases the intelligence of a three-year-old human child) never develop this abstract domain in conceptualizing love, but are able to develop an undifferentiated concept that we might call "love". But notice that even after differentiation occurs in humans, we must still describe love using those metaphorical terms.

If love were an objective non-physical entity that a disembodied process of reasoning simply corresponds to, then we ought to be able to divorce love from the metaphorical language that arises through our embodiment. But, imagine a statement like this:

George loves his wife. He's never felt close to her, he's always put his own needs ahead of hers, and he has always responded to her gestures of affection by withdrawing from her even further.

In what sense does George love his wife? The first sentence seems completely divorced from the second, because those metaphors do not comport with those we use to describe love. Can we describe what it means for George to love his wife without using metaphorical language that is the converse of the above?

Notice too that the metaphors express spatiotemporal relationships. A loving relationship is one in which the partners feel "close"; cold-hearted George is putting his needs "ahead of" his wife's. These metaphors are essential to our description of complex concepts like love, but make no sense if reason could be divorced from our embodiment.

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We've seen how the Aristotlean view fails. It fails to give us an account of how the mind interacts with the world to perceive correspondence, it fails to take into account multiple frames of reference, and it fails to provide a basis for metaphorical thought. So what view could we adopt instead?

Model-dependent realism and physicalism

All of the difficulties with the Aristotlean view disappear if we adopt model-dependent realism, a concept introduced by Stephen Hawking: the idea that there is no model-independent view of reality. Reality, as humans know it, is a construct created through the interaction of the physical world with the gestalt perception of our sensorimotor system and (in turn) the neural structures in our brains. If an objective, perception-independent reality exists, we do not have access to it. Metaphorical language follows from gestalt sensorimotor perception ("that went over my head"), and cognitive abstractions like "love" form from metaphorical thought that arises through differentiated physical experiences.

Those who subscribe to the antiquated Aristotlean view find model-dependent realism highly discomforting. They object that it appears to negate our ability to establish stable truths, since, as Hawking describes in The Grand Design (the book in which he coined the term), no one model is less "real" than any other; instead, what matters is how well the model accounts for known data and allows us to make predictions. Instead of one grand, unified model of the entire universe, we employ a broad range of models that are valid at different frames of reference.

Take again the idea of color. According to the phenomenological frame of reference, the statement "The sky is blue" is objectively true. It reflects a common way in which humans conceptualize color, as well as the way in which we project artificial boundaries onto the world and treat spaces like container-objects (e.g., "the plane is in the sky"). An eliminative physicalist view would say that this is false — there is no "blue" in the sky; all that exists are wavelengths and neural structures. But this viewpoint fails to adequately account for how we conceptualize color and integrate the concept into our language and experience. It is bankrupt for the same reason that the Aristotlean view, with its singular focus on the phenomenological frame of reference, is bankrupt.

Model-dependent realism, then, is a form of what is called non-eliminative physicalism. It is "physicalist" in that it provisionally assumes that all things are ultimately underscored by a physical reality; it posits no mystical entities or undetectable supernatural forces to explain the universe or our interaction with it. But we call something "real" if it accounts for known data and allows us to make predictions; on that view, the term "the sky is blue" is true, because our phenomenological model provides a frame of reference in which it is a meaningful and valid statement.

One of my all-time favorite essays was Sean Carroll's blog post "Free Will Is as Real as Baseball". Without using the term, Carroll is in fact adopting model-dependent realism:

We talk about the world using different levels of description,
appropriate to the question of interest. Some levels might be thought
of as “fundamental” and others as “emergent,” but they are all there.
Does baseball exist? It’s nowhere to be found in the Standard Model of
particle physics. But any definition of “exist” that can’t find room
for baseball seems overly narrow to me. It’s true that we could take
any particular example of a baseball game and choose to describe it by
listing the exact quantum state of each elementary particle contained in
the players and the bat and ball and the field etc. But why in the
world would anyone think that is a good idea? The concept of baseball
is emergent rather than fundamental, but it’s no less real for all of
that.

Likewise for free will. We can be perfectly orthodox materialists and yet believe in free will, if
what we mean by that is that there is a level of description that is
useful in certain contexts and that includes “autonomous agents with
free will” as crucial ingredients.

Carroll is acknowledging that there is a certain frame of reference in which the idea of "free will" makes no sense. There is no room for some sort of "contra-causal" free will in any of the known laws of physics. But there is another frame of reference — our phenomenological one — in which viewing ourselves as rational agents capable of choosing is both valid and necessary. "Free will", in that sense, is as real as any other facet of the human experience.

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But with all these overlapping frames of reference and models of reality that are contingent upon the available evidence, how can we form stable knowledge? The answer lies in our embodiment. Because we are all human beings sharing a similar biological makeup, we conceptualize the world in similar ways — our shared biology is what allows us to communicate shared concepts and metaphors, creating the possibility for shared, stable truths.

Further, we can make use of convergent models that employ different methodologies to account for data but yield compatible results. It's highly improbable, for example, that we'll discover that atoms and molecules do not actually exist since they are employed across a wide range of empirical disciplines that have yielded mountains of valid predictions. The phylogenetic tree at the center of the theory of evolution is likewise supported by multiple independent methods of inquiry: geology, molecular biology, genetics, and paleontology (to name a few). It is highly improbable that all of these lines of evidence can converge and yet still be false, and this gives us confidence in the validity of evolution as a stable truth.

Model-dependent realism gives us the best of both worlds: we can have
stable truths and accept that there is a reality which exists
independently of our ability to perceive it. We can acknowledge many of
the phenomenological experiences central to our humanity as real and
valid, while also acknowledging the physical structure that provides the
basis for it. We can account for metaphorical thought and language,
make sense of abstractions, and close the Aristotlean gap between the
mind and the world.

Post-script

So, why is all this important, anyway? I mean, this post was all kinds of tl;dr, and it was still only a cursory overview of many of these topics. There are complex modern analytical discussions of the correspondence theory of truth which attempt to address the gaps, debates about the formation of metaphor and its place within cognition and language, and on and on. But hopefully this lengthy overview, in which I'm more or less simply attempting to elucidate my own point of view, acts as a springboard for you to see how important these issues are and perhaps sparks some inquiry of your own. If you are that adventurous, I hope you'll share your thoughts in the comments below.